The present invention relates to devices used for dispensing a viscus fluid, and, more particularly, to a device used for injecting a surgical cement into a cavity formed in a bone to secure a prosthesis such as the femoral component in a total hip arthroplasty.
Previously, when it was desirable to fill with a cement a relatively slender cylindrical cavity, the cement was simply poured through the cavity aperture or injected with a standard syringe. In the present practice of orthopedic surgery, a cavity is formed in a bone to receive a prosthetic bone component and a surgical cement is injected into the cavity using an enlarged conventional syringe. More particularly, in the practice of total hip arthroplasty a methyl methacrylate cement is injected into a femoral cavity to secure the femoral prosthesis component of the arthroplasty within the cavity.
Surgeons generally recognize that it is desirable to inject the surgical cement into the femoral cavity by inserting an elongated nozzle to the bottom and injecting the cement so that it flows from the center of the cavity radially to the cavity wall. Furthermore, the nozzle should be withdrawn steadily and continuously to keep the tip of the nozzle at or very near the meniscus of a rising cement column so that the flow of the cement continues to be primarily radial in nature.
Unfortunately, a common technique used by surgeons to inject the surgical cement into the femoral cavity is to use a large volume syringe, including an elongated nozzle, through which the surgeon injects the surgical cement while attempting to maintain the tip of the nozzle at the meniscus of the rising cement column. Since it is very difficult to see down into the femoral cavity during surgery, manual withdrawal of the syringe can only approximate an optimum rate which would maintain the tip at the meniscus and cause radial cement flow to the cavity wall. If the nozzle is retracted too slowly, its tip will fall below the meniscus of the cement and cause the cement to flow both radially and axially along the cavity walls, picking up debris along the rough cavity walls, and not achieving proper bone intrusion. If the nozzle is withdrawn too rapidly, the pressure of the injected cement is too low to achieve proper bone intrusion and air gaps may be formed detracting from the capability of the cement to hold the prosthesis firmly. The magnitude of the problems inherent in the improper injection of surgical cement during orthopedic surgeries is readily apparent when one realizes that such weakening of the cement bond often necessitates corrective surgery.
Accordingly, a device is needed for injecting the cement into the cavity while withdrawing the nozzle of the injection device automatically at the optimum rate for achieving the desired flow of the cement into the cavity and at the desired pressure. Such a device must eliminate the guess work attendant to prior techniques for injecting surgical cement and the device must have the capability to compensate for variations in cavity volumes. The present invention fulfills these needs and provides other related advantages.